1. Field of the Invention
The present invention relates to devices for tensioning a data carrier which is moved by means of feed tractors and which traverses a curved zone between the feed tractors, and in particular to such a device for tensioning a paper sheet in a high speed non-mechanical printer or copier.
2. Description of the Prior Art
A transportation device for conveying a data carrier, such as a paper web in the transfer station of a non-mechanical printer or copier, is disclosed in German OS No. 2,717,315, corresponding to U.S. Pat. No. 4,213,551. The paper web has equidistantly spaced peripheral perforations at its side margins and the transportation device includes feed tractors disposed preceding and following the transfer station about which an endless toothed belt is entrained which engages the perforations and conveys the paper. The feed tractors operate in pairs, with pairs of feed tractors being arranged at the opposite margins of the paper web.
That portion of the data carrier which is disposed between the feed tractors and moves past the transfer station or printing station must be uniformly tensioned in order to achieve accurate image transfer or printing. Factors which operate to introduce nonuniformity into the tensioning of the paper web in the transfer station are: tolerances in the position of the transportation perforations on the data carrier relative to one another as a result of production tolerances, temperature, moisture, and the fact that the data carrier is moved over a curved path in the transfer station thus changing the effective distance between the transportation perforations due to differing thicknesses of data carriers. Such differing thicknesses may be the result of non-uniformities in the thickness of a single-layer data carrier, or by virtue of the use of a multi-layer data carrier.
It is an object of the present invention to provide a device for tensioning a data carrier which is moved by means of feed tractors in which the position of the feed tractors can be matched to different thicknesses of data carriers and the tensioning of the data carrier can be correspondingly modified.
It is a further object of the present invention to provide such a tensioning device which can be utilized when the data carrier traverses a curved zone between the feed tractors in the transfer station of a non-mechanical printer or copier.
The above object is inventively achieved in a tensioning device including a shaft-mounted cam disposed between the wheels of at least one of the feed tractors and which abuts against a bearing element associated with at least one of the wheels in the feed tractor. The wheel associated with the bearing element against which the cam abuts is mounted on a block which is in turn mounted on guide rails which are parallel to the direction of transportation of the data carrier so that by rotating the cam the wheel of the feed tractor is displaced in the direction of transportation of the data carrier thereby adjusting the tension of the data carrier between the adjustable feed tractor and another feed tractor on the same side of the data carrier. The other feed tractor remains in its existing position.
The feed tractor may be constructed in a known manner including two wheels with a transportation belt entrained about the wheels with the shaft having the cam mounted thereon disposed between the two wheels. The cam preferably acts upon a bearing component which is associated with the wheel in the feed tractor which is closest to the curved zone traversed by the data carrier, namely the transfer station.
If a common belt is entrained about the wheels of two feed tractors which are respectively disposed preceding and following the transfer station, rather than two separate belts respectively entrained about each feed tractor, a change in the position of the wheels of the first tractor requires a readjustment of the belt tension in order to tension the data carrier. In this case is preferable to include a further bearing element associated with the other wheel of the first feed tractor, which further bearing component also abuts the cam. The cam is shaped such that upon rotation of the cam the wheels in the first feed tractor are displaced along the guide rails by different amounts.
Each wheel of the first feed tractor may be mounted on a guide block on which the bearing element is also mounted with the guide blocks being slidable along the guide rails in the direction of transportation of the data carrier.
In order to coarsely adjust the position of the bearing elements within the guide blocks, the bearing element is preferably received in a slot in the guide block at a side thereof adjacent to the cam so that the guide block can be set at a position within the slot which permits displacement of the wheels of the feed tractor in a desired range by subsequently rotating the cam.
Identical tensioning devices are embodied in feed tractors comprising a feed tractor pair disposed at the opposite margins of the data carrier. One of the tractors in the tractor pair may be laterally displaceable along axles which are perpendicular to the direction of data carrier transportation so that data carriers of different widths can be accommodated by sliding the feed tractor and tensioning device along the axles until the desired width is obtained.
This device permits adjustment of the tension of the data carrier in the transfer station even when data carriers of different thicknesses are utilized.